I have no experience on either of these boards though looking at them in comparrison.

Custom:
5 of 10 on feel rating. Middle of the road feel not to soft or stiff. soft enough to butter around and play a bit yet stiff enough to charge and bomb runs to an extent.

It's a directional twin camber board that uses light weight wood core. binding mounts are slightly set back to allow the nose to cut through pow and increase flotation and pop on the tail.

Custom X
7 of 10 on feel rating which gives you a slightly more stiff, responsive board that is more stable at higher speeds as well as better edge hold while carving hard.

The Custom X is loaded w/Burton tech. It's A directional twin camber board with a super light wood core "Dragon fly" core which is composed of 500 independent laminations, each individually oriented within the core, result in superior weight-savings, strength, and energized response. This board also features what they call "Multizone EGD" where they strategically input four separate zones, where the wood grain is perpendicular to the core adjacent to The Channel to improve board strength and edge hold. Additionally their "Squeezebox" tech is the use of soft pliable wood under your feet and a harder more ridged wood and the tip and tail for increased maneuverability and board pop. The boards tip and tail has been tapered in thickness to help reduce swing weight for the spin junkies and finally the board is Pre-broke in at factory so you don't have to do it.

So needless to say if it were me looking at these two boards I definitely say the Custom X is worth the extra $100 bones. That's just my opinion feel free to formulate your own. Burton's web site does a good job of explaining all the tech and the reasoning behind it just gotta do the research brotha! good luck, have fun and ride safe.